DOHA, Qatar — When representatives of nearly 200 countries meet in Qatar for annual talks on slowing global warming starting Monday, one of the main challenges will be raising climate aid for poor countries at a time when budgets are strained by financial turmoil.

Rich countries have delivered nearly $30 billion in grants and loans promised in 2009, but those commitments expire this year. And a Green Climate Fund designed to channel up to $100 billion annually to poor countries has yet to begin operating.

Borrowing a buzzword from the US budget debate, Tim Gore of the British charity Oxfam said developing countries, including island nations for whom rising sea levels pose a threat to their existence, stand at a ‘‘climate fiscal cliff.’’

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‘‘So what we need for those countries in the next two weeks are firm commitments from rich countries to keep giving money to help them to adapt to climate change,’’ he said Sunday.

Creating a structure for climate financing has been one of the few tangible outcomes of the two-decade-old UN climate talks, which have failed in their main purpose: reducing emissions of heat-trapping gases that scientists say are warming the planet, melting ice caps, glaciers and permafrost, shifting weather patterns, and raising sea levels.

The only binding treaty to limit such emissions, the Kyoto Protocol, expires this year.